Gas turbine engines, such as those used to power modern commercial aircraft or in industrial applications, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. Generally, the compressor, combustor and turbine are disposed about a central engine axis with the compressor disposed axially upstream of the combustor and the turbine disposed axially downstream of the combustor. For a turbofan gas turbine engine, a large diameter fan is mounted to the engine shaft forward of the compressor. In the turbofan version of the gas turbine engine, a portion of the fan air is delivered to the compressor to pass through the engine core, while the remainder of the fan air passes through a bypass duct thereby bypassing the compressor engine core. Most large commercial jet liners of contemporary design use the turbofan version of the gas turbine engine to power the aircraft.
A nacelle forms a wrap that surrounds the gas turbine engine to provide an aerodynamic housing about gas turbine engine. In a turbofan gas turbine engine, the nacelle includes, from fore to aft, the engine inlet, the fan cowl, the engine core cowl after body and the primary exhaust nozzle. It is customary to provide access doors in various parts of the nacelle to permit service personnel to access various internal components for service, maintenance or replacement. These access doors are mounted on hinge assemblies designed to permit the access doors to pivot outwardly from a closed position to an open position. When in a closed position, the external surface of the access doors must be flush with the external surface of the nacelle to maintain an aerodynamic profile. Therefore, the hinge assemblies supporting the access door for pivotal movement are disposed on the inside of the nacelle body.
Typically, an access door is supported on one side, which is the pivot side, by at least two hinge assemblies. Each assembly includes a hinge arm mounted to the inside of the door and a bracket mounted to the inside of the nacelle body opposite the hinge arm. The distal end of the hinge arm is pinned between the distal ends of a pair of pivot arms mounted to the hinge bracket. A hinge pin extends through a hole in the distal end of the hinge arm in a press fit relationship.
The parts of the doors and hinge assembly are commonly made of aluminum in order to minimize the weight of the assemblies, but the hinge pin is made from a stronger material, such as steel. The end of the hinge pin, being made of aluminum, is prone to wear due to rubbing against the harder hinge pin, which over time causing the hole to elongate, thereby losing its original circular shape and tolerance, thus allowing the door to vibrate. Since fully heat treated aluminum has very poor weldability and exhibits a tendency to lose strength, which cannot be recovered when it is welded, repairing the hinge pin hole by welding is not practical.
Attempts may be made to repair worn hinge arms of this type by inserting a thin-walled, cylindrical bushing into the worn hole. Because the hinge assembly pivots around a hinge pin, the bushing must include an anti-rotation feature to prevent the bushing from rotating within the worn hole of the hinge arm. In conventional practice, the anti-rotation feature has been achieved by staking the bushing to the hinge arm. In conventional practice, staking is typically accomplished by passing a screw or pin from inside the bore of the bushing through the bushing wall into the hinge arm or by driving a screw or pin from one or both end faces of the bushing axially along the interface of the outer wall of the bushing and the bore of the hinge pin. However, these methods require enough structural thickness to be present both in the bushing and in the hinge arm. As hinge assemblies are commonly designed to minimize weight, and therefore material, sufficient parent material may not remain in the strap portion of the hinge arm when the hinge pin hole is overbored to accommodate and support a bushing having the wall thickness necessary for effective staking for anti-rotation by either of the aforedescribed methods. Thus, in many situations, both of the aforedescribed methods are impractical for enduring repair of such worn hinge arms on access door hinge assemblies. For similar reasons, attempts to provide anti-rotation by cementing a thin-walled bushing into the worn hole of the hinge arm using a press-fit or retaining compound have proven impractical.